The autonomic nervous system (ANS) governs the functioning of numerous organs in the body of humans and other mammals. Yet there exists no quick, simple, inexpensive, or reliable test to measure the full range of autonomic function in an individual, nor its current state.
The two major components of the ANS are the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). Nerves from both usually innervate the organs they control. Thus organ performance is the result of the interplay of both PNS and SNS. A measure of either SNS or PNS is not very useful in assessing the condition of the subject. For example, a subject may have high PNS tone without being relaxed because its effects are being offset by high SNS tone. Heart rate, for example, is determined by interplay between PNS and SNS. Both nerves innervate and affect our hearts. When a subject's PNS vagal nerves to the heart are cut, its heart rate rises and remains elevated.
A novel method is described herein to measure the moment-to-moment relative dominance of PNS tone (sometimes also referred to as vagal tone) and SNS tone. The method is inexpensive, easily understood, consistent, reliable, as well as simple and quick to administer. It is completely passive and requires no voltage to be administered to the subject, thus eliminating the possibility of side effects from the resultant current. It works well on both humans and animals.
The method gives a distinctive, “signature” reading for subjects experiencing any moderate to severe pain that has lasted for more than a few minutes, both in humans and other mammals. Therefore, it provides a previously non-existent, objective description of pain. Currently, all pain is now measured by asking the subject questions about their pain (i.e., “On a scale of 0-10, how would you rate your pain?”). This is clearly subjective. Non-verbal patients cannot be evaluated by these methods. Thus health care providers are at a loss to measure pain in young children, advanced dementia adults, some stroke victims and intubated patients, as well as the rest of the animal kingdom. Prey species of animals (including horses and sheep) pose a particular challenge because they are genetically programmed to mask their pain so as not to become the primary target of a predator. Even expensive thoroughbred racehorses are often the subject of vigorous debate by their caretakers regarding their pain status. Furthermore, a reliable and consistent objective measure of pain would prove useful to doctors who suspect the patient is exaggerating or imagining his or her pain, as well as to insurers who suspect malingering.
The method described herein works by recording a measurable physiological correlate of ANS changes, namely the difference in electrical potential between two sensors placed on the skin. Similar to the Tarchinoff voltage measure of electrophysiology, it differs by sensing between sites of similar instead of high to low sweat gland densities. Skin is innervated by nerves from both the SNS and PNS, which, respectively, increase and decrease physiological rates in tissue and organs throughout the body. These nerves are distributed relatively symmetrically throughout the body but are not always activated in a symmetrical manner. With pain, for example, persistent pain from anywhere in the body of moderate to severe intensity begins to raise blood pressure (BP). This activates the baroreceptors in the carotid sinus artery. They trigger an increase in PNS (vagal) tone in an attempt to stop the BP increase and restore homeostasis. In addition, this process triggers the release of endorphins, the body's own, natural opioids, which provide partial pain relief. This process is part of what is known as Descending Nociceptive Inhibitory Control, or DNIC. This response is mediated primarily by the right cardiac vagal (PNS) nerve, not the left one. This nerve branches off and innervates other tissue along the way. The result is slightly slower physiology on the right side of the body. It has now been found that this includes the two-skin-site voltage difference effect. Accordingly, the voltage sensed on the right side of the body, with respect to the left, drops as PNS tone rises through increased activation of the right cardiac vagal nerve.